Bath for treating aluminum and aluminum alloys to form oxide film nonelectrolytically thereon and method for the treatment

ABSTRACT

A bath comprising, as the main liquid, either or both of aqueous hydrogen peroxide solution and aqueous ammonia and additionally incorporating an oxidizing agent, an inhibitor to retard liquid temperature elevation, a stabilizer for solution and, if a heavy metal is present, triethanol amine as a valency stabilizer for said heavy metal, which bath is used for treating the surface of aluminum or an alloy thereof so as to nonelectrolytically form a colored oxide film on the surface. In addition, a method for forming on the said surface a colored oxide film by thoroughly washing the surface of aluminum or an alloy thereof and subsequently immersing the washed metal in the said bath.

United States Patent [1 1 Ito [451 Sept. 16, 1975 BATH FOR TREATING ALUMINUM AND ALUMINUM ALLOYS TO FORM OXIDE FILM NONELECTROLYTICALLY THEREON AND METHOD FOR THE TREATMENT [76] Inventor: Hikaru Ito, 95-20 Katsuragi-machi,

Kishiwada, Osaka, Japan [22] Filed: Apr. 10, 1974 [211 Appl. No; 459,640

[56] References Cited UNITED STATES PATENTS 7/1972 Weaver et a1 148/614 R 8/1972 [to 148/627 Primary Examiner-Ralph S. Kendall Assistant Examiner-John D. Smith Attorney, Agent, or Firm-Oblon, Fisher, Spivak, McClelland & Maier 5 7 4 ABSTRACT A bath comprising, as the main liquid, either or both of aqueous hydrogen peroxide solution and aqueous ammonia and additionally incorporating an oxidizing agent, an inhibitor to retard liquid temperature elevation, a stabilizer for solution and, if a heavy metal is present, triethanol amine as a valency stabilizer for said heavy metal, which bath is used for treating the surface of aluminum or an alloy thereof so as to nonelectrolytically form a colored oxide film on the surface. In addition, a method for forming on the said surface a colored oxide film by thoroughly washing the surface of aluminum or an alloy thereof and subsequently immersing the washed metal in the said bath.

11 Claims, N0 Drawings BATHFOR TR TIN ALUMINUM AND ALUMINUM ALLoYS TO FORM OXIDE FILM NONELECTROLYTICALLY THEREON AND 'METHOD FOR Til-IE TREATMENT BACKGRQUND OF THE INVENTION This inventionrelates to a bath for nonelectrolytically treating the surface'iof aluminum or an alloy thereof, i .e.,'a me'tal 'body consistin g predominantly or totally of aluminum, for thereby forming a colore d oxide film thereon and to a method for forming the col-- ored oxide film on the surface of said metal body.

"In recent years, aluminum and alloys thereof have come to find extensive utility as constructed materials. The demand is particularlystron g for colored products. As techniques for coloring, aluminum and alloys thereof, methods such as are described herein below have been developed. b l v First, the anodic oxidation method will be described.

This method comprises having aluminum undergo anodic oxidation with sulfuric acid serving as anelectrolyte, dyeing the formed oxide film with an organic or inorganic pigment and further sealing pores in the film.. The product obtained bythismethod contains a pig ment which is vulnerableto ultraviolet. rays and, therefore, proves unsuitable for use as exterior construction parts. The product becomes yellow when the anodic oxidation is effected by using oxalic acid as the electro lytic liquid, The product according to this meth od,

however, cannot be obtained inany other color.

When the anodi c oxidation is carried out on .435

(aluminum alloylconsisting of 5.2 percent of Si, 0.75

percent of Fe, 03,1 percent of Cu 0.05 percent of Mg,

0.05 percent of Mn, 0.12 percent of andthe balance to make IOU percent of Al) in sulfuric acid as the electrolytic bath, there is: formedan oxide film having a black color. Because of inferior yield, however, this method now finds practically no utility. As a method for natural color development, there can be cited a method whereby the electrolysis is carried out by using a mixture of an organic acid and an inorganic acidpa mixture of two inorganic acids and a mixture of two inorganic acids and one organic acid as the electrolytic baths, so that the oxide film assumes increasingly darker colors from the amber color finally to the black color. According to this method, the product can be obtained only in a limited range of colors, the power consumption is two to three times as large as that required by the method which effects anodic oxidation of alu minurn by using sulfuric acid as the ,electrolytic solu;

tidn and the electrolytic solution itself :is expensive. All

taken into account, this methodfproves quite expen- I sive. The oxide film obtained by this method, however, has unusually desirable propertiesincluding high resistance to ultraviolet rays from the sun. The chemical methods for oxide film formation sofar developed.in

film, M.B.V. method which gives a gray oxide film and EW method which gives a bluish oxide film. Although the appara tuses employed are invariably simple, the

oxide films produced lack in thicknesses and are on the order of l to 2 microns. In their unmodified forrn,

therefore, these methods do not prove practical. There is also Asadas method. This method comprises forming a silver-white oxide film .of alumite in sulfuric acid as clude AROJIN method which gives a light yellow oxide I lution of metallic salt by way of the secondary electrolysis..However, the oxide film obtained thereby is limited in color to. gold, bronze and black and offers poor resistance to ultraviolet rays compared with the products of most of the methods of natural color develop ment. .Eurther, the operation is complicated and the yield is low. A coating method which also is available for the present purpose forms a coat by applying a resin containing; an added pigment. The coat produced by this method is readily affected by ultaviolet rays from the sun. The method by electrophoretic color development comprises the steps of first forming asilver-white oxide film of alumite by using sulfuric acid as the electrolytic bath and subsequently subjecting the film to electrolysis in a solution of a water-soluble acrylic resin. This method involves many steps of operation,

gives the product in low yields and has a disadvantage.

thatthe film itself is vulnerable to ultraviolet rays.

Among all the methods described above, the method of natural color development excels in terms of development of color.- Nevertheless, this method suffers from the aforementioned disadvantage of high cost.

In recent yearsQmethods for forming colored-oxide films without resorting to electrolysis are under development. For example, the present inventors US. Pat. No. 3,681,149 is concerned with one such method. This method permits a film of aluminum oxide to be formed on the surface of a metal body consisting predominantlyor totally of alumina and further enables color coating to be effected thereon. The bath used for the formation of the. oxide film according to this method has its treating caapacity lowered at such a rate with lapse of time that, in 10 to 20 hours after its preparation, it becomes totally unusable, no matter whether it has served its purpose or it has just been left unused.

Therefore, the bath must be prepared anew prior to each occasion of treatment, greatly increasing the cost of the nonelectrolytic treatment. When a treatment of this sort is carried out on a large commercial scale, it is usual to have the'treatment operation performed daily with an intermission every few hours. According to the method, therefore, the bath must be prepared anew every day, making the production cost increase to a very large extent.

A main object of this invention is to provide an extremely stable and long-preservable bath capable of nonelectrolytically forming an aluminum oxide film on the surface of a metal body consisting predominantly or totally of aluminum.

Another object of this invention is to provide a bath which is capable of forming an oxide film of varying color on the said aluminum oxide. Still another object of this invention is to provide a method for nonelectrolytically forming aluminum oxideon the surface of a metal body consisting predominantly or totally of aluminum by using the aforementioned bath.

Yet another object of this invention is to provide a method for nonelectrolytically forming an oxide film of varying color on the surface of the said metal body.

BRIEF SUMMARY OF THE INVENTION To accomplish the various objects described above,

.thebath of the present invention which serves the purpose of nonelectrolytically forming a film of aluminum oxide on the surface of a metal body consisting preous H solution either individually or simultaneously in the form of amixed solution and additionally incorporating therein'an oxidizing agent such as, for exam ple, KBrOg aloneor, as occasiondemands, in conjunction' with (NH CO ','aninhibitor such as, for example, KF, or-NHQCI or sorbital which is capable of retarding the bath temperature increase and "preventing the formed hydroxide from dissolution and-triethanol amine which functions as'a bath stabilizer. If thebath containsa heavy"'-m'etal", the triethanol amine functions as the valency stabilizer of the said heavy metal. This invention also embraces a method fof treating thesur face of the said'mtal body with the aforementioned bath so asto-form a film of aluminum oxide thereon. A bath which additionally incorporates at least one kind of heavymetal salt in the aforementioned bath as the agentfor producing a film of aluminum oxide in a varying color and a method for producing the colored oxide film by the use of such bath are also embraced by the present invention. The present invention isparticularly characterized by the addition to the bath composition of triethanol amine which brings abouta heretofore unattained effect of enabling the bath to'be'preserved stably fora long time. Thus, 'an inexpensive and practical method of nonel'ectrolytic treatment has been realized. Other characteristics and other benefitsof this invention-will be described in further detail below.

DETAILED DESCRIPTION OF THE INVENTION Table 1 the colored film of aluminum oxide and also provides a method forforming a colored film of oxide on the surface of aluminum a; n alloy "the eof by; the, use of said bath The characteristics of this invention will ,be described in detail hereinbelow. s

The novel bath for the purpose of this invention isa mixed aqueous solution using aqueous ammonia alone or aqueous hydrogen peroxide solution alone or 7 a mixed solution thereof and additionally incorporating an oxidizing agent, an inhibitor serving to, retard the bath temperature increase an inhibitor for preventing the produced hydroxide from dissolution and triethanol amine. Thetreatment give in this bath for the formation of the colored oxide film on the surface of aluminum or an 'alloy'thereof is carried out for a short length of time of 20 to 30 minutes. This treatment gives rise to a colored oxide film having a thickness of 5 to l 1 microns. H i I In this treatment, a film of aluminum hydroxide is first formed on the surface of "the metal body and the,

formed film is dehydrated by the oxidizing agent to produce a wall-white oxide filmconsisting of A1 05. iln this case, since the aqueous solution contains the inhibitor added in advance for the purpose of preventing the formed hydroxide from dissolution, the hydroxide is not dissolved but is dehydrated by the oxidizing agent.

Where oxide films of varying fine colors are desired, it suffices to have saltsof varying heavy metals dis solved in advance in the bath. When the metal body mentioned above is immersed in the bath incorporating the salt of heavy metal, the hydroxide of said heavy metal is formed simultaneously with the film of alumi that a film of oxide having a color peculiar to the par- Typical chemical analyses of aluminum and alloys thereof Designation 8K7!) Fe(7() CuU/z) Mm /1) Mg(7() 'Zn(/:) CrU/r) TiU/z) AU/r) Balance to 28 0.l2 0.38 0.09 tr. 0.03 v make 1007: 0.4] 0.7l 0. l 7 0.09 0.85 0.05 0.02 52S 0.l l 0.34 0.05 0.03 2.51 0.04 0.20 63S 0.45 0.08- 0.07 0.7l 0.04 0.05

Aluminum or an alloy thereof is first defatted by im mersing it in a 5 percent neutral detergent solution at 50 to C, then washed with water, subsequently etched'by immersion in a 5 7 wt percent aqueous NaOH solution for 5 to 10 minutes, washed again with water and then immersed in a 20 25 wt percent nitric acid solution for 5 to 7 minutes. Finally, the metal surface is cleaned by thorough washing'with water and thereafter immersed in a bath of the prescribed composition for the formation of a colored film of oxide for a fixed length of time at a fixed temperature. Consequently, the film of oxide is formed'on the surface of I the metal body. s

The metal body is subsequently washed with water,

cleaned with pure water at 50C, subjected to'so-calld clear coating with a urethane resin to a thickness of 10 microns and finally dried by baking at 140C for 1 minutes.

In the foregoing stages ofth'e process, the present invention provides a novel bath to be used-for forming ticular kind of heavy metal willbe formed on the. su rface of the metal body. In this case, the inhibitor in- I vated in temperature. In addition, the bath also contains ammonia, an oxidizing agent, hydrogen peroxide and a heavy metal. When the bath is composed solely of these components, it is chemically so unstable that if it is allowed to stand in its unaltered form after its preparation, it will no longer function as desired after several hours of standing. Further, when the treatment of the alloy in such bath is'repeated, the bath readily undergoes decomposition and becomes unusable in a short period of time. This isbecause, if the bath happens to contain the salt of a heavy metal, it has its chemical composition changed in consequence of the variation of the valency of the heavy metal such as, for CO-H- (oridutum) CO+++, F (nnllalion) F C such change of thechemical composition of the bath, the present invention incorporates in the bath the aforementioned inhibitor for retarding the bath temperature increase and triethanol amine as a stabilizer serving to prevent possible change of the valency of the i said heavy metal. Because of the presence of these additives, the bath can stably be preserved over a long time for use in the subsequent cycles of treatment. Further, the bath can have its properties retained intact after the treatment, or after it has been used in repeated treatment or in intermittent operation where the treatment regularly started and stopped at fixed time intervals; The bath, once produced, remains stable and permits use until its ultimate exhaustion. In this sense, the present invention is quite advantageous from the commercial point of view. it allows the treatment of the formation of oxide film to be carried out on an inexpensive, full production scale. 3

As the inhibitor for retarding the bath temperature elevation and as the inhibitor for preventing dissolution of the hydroxide, there are used KF, NH CI and sorbitol. If (NH CS is added as occasion demands, then the ratio of filmformatio'n is uniformized. As the oxidizing agent, there is used KBrO either alone or, as the circumstance requires, in conjunction with (NH CO Addition of thisoxidizing agent is effective in stabilizing the bath or maintaining the bath at its proper pH range.

The oxide film or the film of A1 which is obtained by performing the treatment in a bath containing no heavy metal salt has a plaster-white color. By adding to this bath the salt of a heavy metal, however, the formed oxide film can be made to assume a color peculiar to the particular kind of the heavy metal as will be described afterward.

The effect of this invention will be demonstrated by citing herein below preferred embodiments of this invention and comparative examples. The preferred embodiments should be interpreted as illustrative and not in any limiting sense.

EXAMPLE 1 A bath for the treatment was prepared by mixing 470 cc of 28 percent l.5N NH OH solution, 30 cc of 32 percent aqueous H 0 solution, l0.0g of KF, 8.0g of NH CI, 1.5g of KBrO 5.0g of (Nl-l CO and 0.2g of sorbitol and 5 cc of (OHCH CH N.

25 plates having a surface area of 0.5 dm were washed on the surface by the conventional method. a. First, seven of the 25 plates (total surface area of 3.5 dm were immersedfor minutes in the aforementioned bath at 20 C so as to produce coats of the oxide (film thickness 5.2 7.3 ,u) thereon. Then the 28 plates were removed from the bath.

b. Separately, 10 of the 28 plates (total surface area of 5 dm) were subjected to the same treatment asthat of (a) for minutes so as to produce coats of the oxide 7.5 9.5 ,u in film thickness thereon. Similarly, five moreof the 25 plates (total surface area 2.5 dm were treated for 20 minutes to produce coats of the oxide 5.7 7.9 ,u. in film thickness. Thus, a total of twenty-two 28 plates (total surface area 1 l dm were treated. The bath was cooled to l 1C and left to stand for 18 hours.

Thereafter, the bath was heated to 20 25C and used for the treatment of additional 28 plates: Five 28 plates (total surface area 2.5 dm were immersed therein for 20 minutes to produce coats of the oxide 5.6 7.4 y. in film thickness and five more 28 plates (total surface area 2.5 dm were left to stand therein for 30 minutes to produce coats of the oxide 7.7 9.0 p. in film thickness. Thereafter, the bath was cooled to 12C and left to stand for 22 hours. After standing for said period, the bath was continuously used in the cycles of treatment described below. The conditions of the treatment and the results thereof were as follows: Eight plates (4 dm after 20 minutes of immersion, pro duced coats 5.5 7.0 p. thick, five plates (2.5 dm after 30 minutes of immersion, produced coats 7.6 9.3 ,u. thick and five plates (2.5 dm after 20 minutes of immersion, produced no coat. From this, it is seen that a total of 45 aluminum plates having a surface area of 0.5 dm could be effectively treated with about 500 cc of the bath, with the film thickness ranging between 5.2 and 7.4 ,u. for '20 minutes immersion and between 7.5 and 9.5 p. for 30 minutes immersion respectively. The period between the time the bath was prepared and the time the bath became totally unusable was 43 hours 20 minutes, which consisted of a total of 200 minutes during which the bath contained the plates for treatment and 40 hours during which the bath stood at rest.

The 28 plates on which colored films of oxide had thus been formed were finished as products by being subjected to the subsequent treatments such as washing with hot water and cold water, drying and, if occasion demands, clear coating and finally drying by roasting to be performed by known techniques.

Similarly 55 plates and 63S plates were subjected to the same treatment. The results were as shown below.

Range of film thickness 5.6 8.0 y. for 20 minutes immersion 7.6 10.1 a for 30 minutes immersion Total number of plates treated 4| plates (20.5 dm

COMPARATIVE EXAMPLE l A bath entirely the same as that of Example 1 was prepared, except for omission of the addition of (HOCH CH );,N. After the preparation of this bath, the treatment was repeated on 25 plates by following the procedure of Example 1. The bath became totally unusable after 20 hours of the treatment. A total of twenty-seven 25 plates having a total surface area of 13.5 drn could be treated effectively. Comparision of Exammple 1 and Comparative Example 1 clearly indicated the effect of the incorporation in the bath of (HOCl-I CH N.

EXAMPLE 2 -A bath prepared by mixing 50 cc of 28 percent aqueous NI-I OI-I solution, 70 cc of 32 percent aqueous H solution, 380 cc of H 0, 10.0g of KF, 5.0g of NH CI, 1.0g of KBrO 1.5g of Na Cr O 0.1g of sorbitol and cc of (HOCH CH N was first maintained at 20 23C. Treatment entirely the same as that of Example 1 was repeated on 2S plates (having a surface area of 0.5 dm as follows: The immersion time was 30 minutes per cycle. (1) A total of six plates (3 dm were treated in three separate cycles. (2) The bath was cooled to 1 1C and left to stand at rest for 18 hours. (3) It was heated to 20C to permit a total of five plates (2.5 dm to be treated in two separate cycles. (4) The bath was cooled to 12C and left to stand at rest for hours. (5) It was heated to C and then used for treating a total of six plates (3 dm in three separate cycles. (6) It was cooled to l 1C and then left to stand at rest for 19 hours. (7) The bath was heated to 20C and used for treating a total of five plates (2.5 dm in five separate cycles. (8) It was cooled to 12C and thereafter left to stand at rest for 18 hours. (9) The bath was used for treating a total of five plates (2.5 dm in two separate cycles. Thus, a grant total of twenty-seven plates were treated in the bath to produce films of oxide, with film thicknesses ranging between the minimum of 5.6 ,u. and the maximum of 10.8 [.L. The color of the films was yellow. The total period between the time the bath was prepared and the time the bath became-entirely exhausted was 77 hours 30 minutes, which consisted of a total of 450 minutes during which the bath contained the plates for treatment and 70 hours during which the bath stood at rest. Entirely the same treatment using the same bath was repeated on 635 plates. A total of twenty-five plates could be treated to produce films of oxide, with film thicknesses ranging between 6.2 p. and 11.3 p

COMPARATIVE EXAMPLE 2 A bath having exactly the same composition as that of Example 2 was prepared, except for omission of the incorporation of (HOCH CI-I N. When the treatment using this bath was carried out by faithfully repeating the procedure of Example 2, the bath became unstable after lapse of 10 hours of time after its preparation. Thereafter, no film of oxide was formed on plates immersed in the bath. When the same bath was left to stand unused for ten hours and thereafter put to use, it did not produce the film of oxide at all on the plates.

EXAMPLE 3 A bath was prepared by using 450 cc of 28 percent 3N NH OH solution, 50 cc of 32 percent aqueous H O solution, 10.0g KF, 3.0g of Nl-I Cl, 0.1g of KBrO 1.0g of sorbitol and 3 cc of (HOCH CI-I N. With this bath, 52S plates were treated as follows under entirely the same conditions as used in Example 1: (1) The bath was used for treating plates in four separate cycles. (2) It was cooled to 1 1C and then left to stand at rest for 17 hours. (3) It was heated to 20C and used for treating plates in four separate cycles. (4) It was cooled to 11C and left tostand at rest for hours. (5) It was heated to 20C and used for treating plates in four sepa- .rate cycles. (6 The bath was cooled to 12C and then left to stand at rest for 19 hours. (7) It was heated to 20C and used for treating plates in four separate cycles. The total period between the time the bath was prepared and the'time it became totally exhausted was 69 hours 40 minutes, which consisted of a total of 520 minutes during which the bath contained plates for treatment and 61 hours during which the bath stood at rest. The treatment produced films of oxide, with film thicknesses ranging between 4.7 and 6.3 p. for 20 minutes immersion and between 7.6 and 9.8 p. for 30 minutes immersion respectively. In the case of 63S plates, the treatment by 20 minutes immersion produced films of oxide on a total of 22 plates, with film thicknesses ranging between 5.6 and 7.8 p. and the treatment by 30 minutes immersion enabled a total of 22 plates to be coated with films of oxide, with film thicknesses ranging between 8.0 and 10.3 ,u. In this case, the bath remained effective for a total period of 74 hours, which consisted of 550 minutes during which the bath contained plates for treatment and 65 hours during which the bath stood at rest. The films of oxide produced here had a reddish brown color.

COMPARATIVE EXAMPLE 3 A bath was prepared by using the same components as those of Ecample 3, except for omission of the addition of (OHCH CI-I N. On lapse of about 10 hours after its preparation, the bath became unstable and incapable of producing films of oxide, no matter whether it was used for the treatment or it was left to stand at rest during the period.

EXAMPLE 4 A bath was prepared by using 500 cc of 28 percent 3N NH OH solution, 10.0g of KF, 5.0g of NH CI, 2.5g of NH F-l-IF, 1.2g of KBrO 1.0g of (NI-I CS, 0.7g of CoCl 0.5g of CuCl 0.1g of sorbital and 5 cc of (HOCH Cl-I N. The treatment with this bath was performed on 28 plates as follows under entirely the same conditions as in Example 1. (1 The bath was used for treating plates in three separate cycles. (2) It was cooled to 12C and then left to stand at rest for 27 hours. (3) It was heated to 20C and used for treating plates in four separate cycles. (4) It was cooled to 1 1C and then left to stand at rest for 23 hours. (5 The bath was heated to 20C and vused for treating plates in four separate cycles. (6) It was cooled to 1 1C and then left to stand at rest for 18 hours. (7) It was heated to 20C and used for treating plates in three separate cycles.

The total period between the time the bath was prepared and the time it became totally unusable was 73 hours 50 minutes, which consisted of a total of 350 minutes during which the bath contained plates for treatment and 68 hours during which the bath stood at rest. The treatment produced films of oxide, with film thicknesses ranging between 5.2 and 7.0 p. for 20 minutes immersion and between 7.5 and 9.5 p. for 30 minutes immersion respectively. In the case of 63S plates, the same bath remained effective for a total period of 81 hours 20 minutes, which consisted of a total of 320 minutes duringwhich the bath contained plates for treatment and 76 hours during which the bath stood at rest. The films of oxide produced in this treatment had film thicknesses rangingbetween 5.7 and 7.3 u for 20 minutes immersion and between 7.9 and 9.3 p. for 30 .9 minutes immersion respectivelyflhe color of the films of oxide was light greenish brown. i

COMPARATIVE EXAMPLE 4 A bath was prepared by using the same components as those of'Examp le 4, except for omission of the additon of (HOCl-l Cl- 1 N. This bath became entirely exhausted on lapse of about 20 hours. after its preparation, no matter whether the bath was used for the treatment or it was left to stand at rest during the period.

EXAMPLES 5 12 compositions as those of Examples 5 -l2, except for omission of the inclusion of (OHCH- CH N. With these baths, the treatment was carried out by faithfully repeating the procedure described. On lapse of 10 to hours after their preparation, they became unusable. When the same baths were left to stand idly for several hours, they similarly became entirely. unusable.

It is clear from comparison of Examples 5 12 and Comparative Examples 5 12'that inclusion of (OHC- H CH N great1y stabilizes the bath which contains a heavy metal and is also effective in stabilizing the bath which does not contain any heavy metal and that this amine helps to add to the thickness of oxide film formed Thus, this invention has really profound significance from the viewpoint of practical use.

What is claimed is:

Chemical composition of bath COMPARATIVE EXAMPLES 5 12 Baths were prepared by using respectively the same Exu' mplc NH ,Ol-l H. .O.' KF( g) N H Cl KBrQ, NH F.HF (NH. .CS CuCl A (g) (g) (g) (g) (g) s 28 /r 3N -450cc= 32 cc 10.0 ,1 y 3.0 1.0 6 289? 3N 500cc 10.0 5.0 1.2 1... 0.3 0.1 7 2871 3N 500cc 12.0 5.0 0.5 0.5 t 1.2 8 28% 500cc .12.0 4.5 0.7 0.5 0.3 9 2m 3N500cc 12.0 5.0 0.5 0.7 1.2 1.0 10 2871 3N cc *1 7.0 3.0 6.0

100cc 1 1 28V: 3N 500cc 10.0 5.0 0.7 0.5 0.1 12 21-171 3N 500cc 10.0 5.0 1.2 1.2

Total Tri- Temp Time Desig- Film Numarea Color her CoCl. KMnO, Sorhitol ethanol nation thickness of of min) amine (C plate plutc (g) (g) (g) (q) (dm 1.0 0.1 2 20-23 20 2S 5.6-7.3 27 13.5 Pink 30 8.8-11.0 2.5 0.1 2 20-23 20 23 63-70 25 12.5 Amhcr 30 7.5-9.1 0.1 2 20-23 20 2S 5.6-8.0 21 Brown 30 8..-12.7 20 5S 6.3-8.3 23 11.5 30 9.3-1l.5 20 635 4.9-7.2 25 12.5 30 7.7-9.7 1.2 0.1 5 20-23 20 2S 7.3-10.5 26 13.0 Black 20 635 6.8-9.4 25 12.5 2.0 0.1 5 20-23 20 2S 5.7-7.2 27 13.5 Bronze 30 8.1-9.8 1.0 0.1 2 20-23 20 2S 5.9-8.7 21 10.5 Gold 20 63S 6.2-9.3 22 1 1.0 0.9 0.1 5 20-23 20 2S 5.3-7.2 31 15.5 Olive t 30 7.6-9.0 0.7 0.5 5 20-23 20 225 5.2-9.7 31 15.5 Lead- 2o 63S 53-101 29 14.5 gray "Water 1. A bath for nonelectrolytically forming a colored aluminum oxide film on the surface of metal body consisting at least predominantly of aluminum, which bath is an aqueous solution Consisting essentially of 1.0 3.0 N aqueous ammonia, 0.3 6.0 g/500 cc of KBrO as an oxidizing agent, 6 12 g/500 cc of KF, 2.5 8.0 g/500 cc of NH C1 and 0.05 0.50 g/500 cc of sorbitol, whereby said KF, NH C1 and sorbitol are inhibitors for retarding the elevation in bath temperature and for preventing the dissolution of the hydroxide first formed on the surface of said metal body when contacted with said bath and 1.5 5.0 cc/500 cc of triethanol amine.

2. A bath according to claim I, wherein an aqueous solution of g/500 cc (Nl-l CO is additionally incorporated as an oxidizing agent.

3. A bath according to claim'l, wherein an aqueous solution of 0.2 1.2 g/500 cc (NH CS is additionally incorporated as an inhibitor serving to retard the bath temperature elevation and prevent the hydroxide from dissolution.

4. A bath according to claim 1, wherein an aqueous solution of 0.6 3.0 g/500 cc of a heavy metal salt is additionally incorporated.

5. A bath according to claim 4, wherein the heavy metal salt is selected from the group consisting of Na Cr O CuC1 CoCl and KMnO 6. A bath according to claim 1 wherein an aqueous solution of 6 10 percent hydrogen peroxide is additionally incorporated as an oxidizing agent.

7. A method for nonelectrolytically forming a colored aluminum oxide film on the surface of a metal body consisting at least predominantly of aluminum I 12 which method comprises treating said surface with a bath which bath is an aqueous solution consisting essentially of 1.0 3.0 N aqueous ammonia, 0.3 6.0 g/50O cc of KBrO as an oxidizing agent, 6 12 g/50O cc of KF, 2.5 8.0 g/500 'cc of NH C1 and 0.05 0.50 g/500 cc of sorbitol, whereby said KF, NH C1 and sorbitol are inhibitors for retarding the elevation in bath temperature and for preventing the dissolution of the hydroxide first formed on' the surface of said metal body when contacted with said bath and 1.5 5.0 cc/500 cc of triethanol amine, thereby forming aluminum hydroxide on said surface and concurrently dehydrating saidaluminum hydroxide to form aluminum oxide.

8. A method according to claim 7, wherein an aqueous solution of 0.2 1.2 g/500 cc (NH CS is additionally incorporated as an inhibitor for retarding the bath temperature elevation and preventing the hydroxide from dissolution.

9. A method according to claim 7, wherein an aqueous' solution of 0.6 3.0 g/SOO cc of a heavy metal salt is additionally incorporated.

10. A method according to claim 7, wherein the heavy metal salt is selected from the group consisting of Na Cr O CuCl CoCl and KMnO 11. The method according to claim 7, wherein an aqueous solution of 6 10 percent hydrogen peroxide is additionally incorporated as an oxidizing agent. 

1. A BATH FOR NONELECTROLYTICALLY FORMING A COLORED ALUMINUM OXIDE FILM ON THE SURFACE OF METAL BODY CONSISTING AT LEAST PREDOMINANTLY OF ALUMINUM, WHICH BATH IS AN AQUEOUS SOLUTION CONSISTING SSENTIALLY OF 1.0 - 3.0 N AQUEOUS AMMONIA, 0.3 - 6.0G/500CC OF KBRO3 AS AN OXIDIZING AGENT, 6 - 12G/500 CC OF KF, 2.5 - 8.0G/500 CC OF NH4CI AND 0.05 - 0.50G/500 CC OF SORBITOL WHEREBY SAID KF, NH4CI AND SORBITOL ARE INHIBITORS FOR RETRADING THE ELEVATION IN BATH TEMPERATURE AND FOR PREVENTING THE DISSOLUTION OF THE HYDROXIDE FIRST FORMED ON THE SURFACE OF SAID METAL BODY WHEN CONTACTED WITH SAID BATH AND 1.5 - 5.0 CC 500 CC OF TRIETHANOL AMINE.
 2. A bath according to claim 1, wherein an aqueous solution of 5g/500 cc (NH4)2CO3 is additionally incorporated as an oxidizing agent.
 3. A bath accordiNg to claim 1, wherein an aqueous solution of 0.2 - 1.2 g/500 cc (NH2)2CS is additionally incorporated as an inhibitor serving to retard the bath temperature elevation and prevent the hydroxide from dissolution.
 4. A bath according to claim 1, wherein an aqueous solution of 0.6 - 3.0 g/500 cc of a heavy metal salt is additionally incorporated.
 5. A bath according to claim 4, wherein the heavy metal salt is selected from the group consisting of Na2Cr2O7, CuCl2, CoCl2 and KMnO4.
 6. A bath according to claim 1 wherein an aqueous solution of 6 - 10 percent hydrogen peroxide is additionally incorporated as an oxidizing agent.
 7. A method for nonelectrolytically forming a colored aluminum oxide film on the surface of a metal body consisting at least predominantly of aluminum which method comprises treating said surface with a bath which bath is an aqueous solution consisting essentially of 1.0 - 3.0 N aqueous ammonia, 0.3 - 6.0 g/500 cc of KBrO3 as an oxidizing agent, 6 - 12 g/500 cc of KF, 2.5 - 8.0 g/500 cc of NH4Cl and 0.05 - 0.50 g/500 cc of sorbitol, whereby said KF, NH4Cl and sorbitol are inhibitors for retarding the elevation in bath temperature and for preventing the dissolution of the hydroxide first formed on the surface of said metal body when contacted with said bath and 1.5 - 5.0 cc/500 cc of triethanol amine, thereby forming aluminum hydroxide on said surface and concurrently dehydrating said aluminum hydroxide to form aluminum oxide.
 8. A method according to claim 7, wherein an aqueous solution of 0.2 - 1.2 g/500 cc (NH4)2CS2 is additionally incorporated as an inhibitor for retarding the bath temperature elevation and preventing the hydroxide from dissolution.
 9. A method according to claim 7, wherein an aqueous solution of 0.6 - 3.0 g/500 cc of a heavy metal salt is additionally incorporated.
 10. A method according to claim 7, wherein the heavy metal salt is selected from the group consisting of Na2Cr2O7, CuCl2, CoCl2 and KMnO4.
 11. The method according to claim 7, wherein an aqueous solution of 6 - 10 percent hydrogen peroxide is additionally incorporated as an oxidizing agent. 